As an undergraduate at Harvard, Richard Lyman Bushman was offered some friendly advice by a favorite professor: he was a fine student, but his Mormonism was seen by the Harvard establishment as a “bunch of garbage.”

Mr. Bushman would do himself a favor, the professor told him, to leave the Church of Jesus Christ of Latter-day Saints behind as a relic of his upbringing.

“I reacted just the opposite,” Professor Bushman said in a phone interview. “I said, ‘You’re not going to bully me, you big representative of Harvard culture.’ ”

That was 57 years ago. Since then, Professor Bushman has retained his Mormon faith even while forging an Ivy League academic career, earning posts at Columbia and Harvard.

In fact, as his teaching and research focused on colonial American history, Professor Bushman also managed to become something of an ambassador for Mormonism to the outside world....